This invention generally relates to MIS field effect devices and in particular concerns the insulating material used between discrete transistors found in such devices.
A MIS (metal-insulator-semiconductor) device includes a semiconductor substrate, an insulating layer on the substrate, and a gate electrode disposed on the insulating layer. The insulating layer in prior art devices is usually an oxide, and the devices are usually called MOSFETs (metal-oxide-insulator field-effect-transistors). With a MOS field-effect device, additional source and drain electrodes are disposed to either side of the gate electrode and a lateral current may be caused to flow between the source and drain electrodes through application of proper bias potential to the gate electrode. Specifically, in the "enhancement" mode, application of a biased potential to the gate produces a conducting layer beneath the metal oxide allowing lateral current flow between the source and drain electrodes. In the "depletion" mode of operation, application of a bias potential to the gate electrodes produces an insulating region between the source and drain electrodes which serves to decrease current conduction.
MOS devices, when exposed to ionizing radiation such as would occur in a space environment, suffer radiation damage in the form of charge trapped in the oxide and/or at the oxidesemiconductor interface and undergo various changes in the electrical characteristics thereof. The circuits in which these MOS devices are found become unstable and in some instances are actually rendered inoperative. A MOSFET device with a substantially improved useful life when subjected to a radiation environment is sorely needed.
Prior work in this area includes U.S. Pat. No. 3,799,813 to Danchenko which discloses a technique for radiation hardening of MOS devices by the introduction of boron into the insulating oxide. While this patent is suitable for its intended purpose, it does not provide the simplicity and degree of protection that the present invention provides, nor does it involve the use of the same insulating material.